The present invention relates in general to background monitoring of an RDS radio broadcast for traffic announcements, and more specifically to a search strategy for selecting a traffic capable station to be monitored when reproducing other audio media such as a cassette tape, compact disk, or a radio station without traffic capability.
Radio data systems such as the RDS system in Europe and the radio broadcast data system (RBDS) in the United States transmit auxiliary information with the radio broadcast including a traffic capable (TP) flag to identify broadcast stations which carry traffic announcements and a traffic announcement (TA) flag for identifying that a traffic announcement is currently being transmitted by the broadcast station. Other RDS flags are transmitted to identify emergency alert messages, news broadcasts, and weather announcements, for example. These flags allow a radio receiver to be tuned to a broadcast station that provides traffic information for a driver of an automobile. In addition, a radio receiver can monitor a traffic capable station during times that the audio system is reproducing audio signals from a source other than a traffic capable radio station (such as a cassette tape or compact disk; or even an AM radio station or a non-capable FM radio station if a separate radio tuner is available).
By monitoring the flags of a traffic capable station in the background while the audio system reproduces audio signals from other media, it is possible for the audio system to automatically switch to the traffic announcement when one is present thereby keeping the driver of a vehicle informed of traffic developments while driving. Whenever listening to an audio source which is not a traffic capable broadcast station, a search strategy must be adopted to find an appropriate broadcast station to be monitored in the background. If the last broadcast station to which the tuner was tuned before switching to the alternate media is not a traffic capable station, then a different station must be selected automatically by the receiver. Prior art receivers typically perform a standard station scan to find an RDS station transmitting the TP flag and have used either the first traffic capable station which is found or the strongest traffic capable station found during a search of the complete band.
A broadcast station which is traffic capable may or may not satisfy the individual preferences of an individual driver. The format, language, frequency, or coverage area of traffic announcements from various stations will vary. Therefore, an arbitrary search for a traffic-capable broadcast station can easily fail to provide the most optimal station for matching the preferences of any individual driver.